mysql语句中变量

-- 定义用户定义变量
SET @myVariable = 10;

-- 使用用户定义变量
SELECT * FROM myTable WHERE id > @myVariable;

-- 定义并使用局部变量（在存储过程中）
DELIMITER //
CREATE PROCEDURE myProcedure()
BEGIN
  DECLARE localVariable INT;
  SET localVariable = 5;
  SELECT * FROM myTable WHERE id > localVariable;
END //
DELIMITER ;

-- 调用存储过程
CALL myProcedure();

-- 查看系统变量
SHOW VARIABLES LIKE 'max_connections';

-- 修改会话变量
SET SESSION max_connections = 200;

SET @myVariable = 10;
SELECT * FROM myTable WHERE id > @myVariable;

DELIMITER //
CREATE PROCEDURE myProcedure()
BEGIN
  DECLARE localVariable INT;
  SET localVariable = 5;
  SELECT * FROM myTable WHERE id > localVariable;
END //
DELIMITER ;

-- 查看变量是否可修改
SHOW VARIABLES LIKE 'max_connections';

-- 修改全局变量（需要管理员权限）
SET GLOBAL max_connections = 200;